It's an interesting week that sees Vince Cable accused of being a socialist (by the Tory donor Adrian Beecroft) and Nick Clegg accused of "communist tactics" (by the headmaster of a private school, Tim Hands). What would Marx say? (Coincidentally, I have this written on my mug.) Leaving Cable's firebrand trottery aside for a second, Clegg's Stalinism stems from his speech on social mobility, to launch the Sutton Trust's report.

The figures in this report are stark but unsurprising – one child in five is on free school meals, but only one in 100 Oxbridge entrants is; that's probably the most arresting statistic in terms of how poverty suffocates one's prospects. Just as enraging is the fact that only 7% of children attend private schools, but these schools provide 70% of high court judges.

Nick "Commie" Clegg concludes that the government needs some targets; except because that word is so last century, they now talk of "annual trackers" – 17 measures, including the number of A to Cs in GCSE results among children on free school meals, and participation in higher education of those from poorer backgrounds.

Tim Hands' objection is that if factors such as background are taken into account by universities, it will be commensurately harder for kids from great privilege to get into Oxbridge. He calls this "capping the achievements of pupils in independent schools".

I think he's a really good example of my new theory; just as privatised medicine leads to the over-treatment of the rich and under-treatment of the poor, private schools over-educate the rich. This leads to many of them being educated beyond their intelligence.

It's a precarious, unenviable position, particularly for those with enough dog sense to be aware of it. When the suggestion is made that universities should broaden their criteria, and look at factors beyond a pupil's accent and how many times they've read the Iliad, you can hardly blame the insecure creatures of privilege for freaking out.

Social mobility sounds unarguable, but like so many other ideas that are apparently self-evident – the primacy of the "hard-working family", the ubiquity of "generations of worklessness" – its apparent simplicity is a cover. It's not Clegg's fault, incidentally: social mobility has been a policy-wonk buzzword for as long as child poverty targets have been in place – targets which, incidentally, will not be met.

This brings me to my first point: you can call it a target or a tracker, but this school of governance – imagine your ideal outcome, plot the signs that your outcome is being achieved, codify those signs into a "target", but never actually change anything – doesn't work. The child poverty targets weren't achieved because no serious attack was made on income inequality.

The social mobility "trackers" will most probably lead to the blaming of schools in poor areas, as they try to achieve those five A to Cs for disadvantaged kids; schools will learn to game the system, resulting in grade inflation; there will be an annual ding-dong with rectors from Oxford and Cambridge as it emerges that they've managed in yet another year not to find a single black person clever enough to study history. And that will be that. No serious change will occur because no serious policy lies behind the call for change.

Moreover, even if social mobility was achieved, what is so great about a society in which the outliers of each class can move relatively freely up and down the hierarchy? What's so great about being able to escape the gutter, when the bulk of people are still in it?

Part of the reason that class has become so ossified is that, in this time of great inequality, the consequences of dropping from any given class to the one below it are severe – you would move heaven and earth to prevent your children fetching up in blue-collar employment when wages at the bottom are no longer enough to live on. No wonder people try to lock in their privilege by paying for education. The only rational solution to that is to work towards a time when there is less difference between the classes.

This new-soft-left alternative, where you fix it to fast-stream the clever kids out of deprivation, leaving the rest to blame themselves for their shabby prospects because they turned out not to be clever enough … well, obviously it's not what any sensible person would call communism. It's not what you'd call socialism either. It's not liberal egalitarianism, or any of those more fine-tuned theories that make it possible to be a leftie and still own a house. It's not left wing and, fundamentally, it doesn't make anything any better.

Even if the waters of the social fountain were in perpetual motion (and you can bet that Clegg doesn't mean that by "social mobility" – he's talking about other people's kids having the freedom to rise, not his own having the potential to fall), you'd still have to accept, even embrace, the idea of some people living and dying in the sludge. Who could ever line up behind such a laughably shoddy vision of the future, a world in which everything looks roughly the same, but each class has had a very slight reshuffle in personnel?

This debate, as it's framed by the coalition – do you believe in social mobility, or do you believe in sink or swim? – is bankrupt (like so much else). I don't believe in either.